#8 Casein Kinase 2 Catalytic Subunits a1/a2 of the SSU Processome’s UTP-C Sub-Complex Regulates Growth Likely through Ribosome Biosynthesis
James JL Cluff, Brandon University; J. Michael Charette, Brandon University
The nucleolus, the site of ribosome assembly, is a diagnostic and prognostic marker of cancer. However, the contribution of ribosome assembly to cancer has only recently been uncovered. It is now known that cell growth is directly dependent on the rate of ribosome biosynthesis and that ribosome assembly defects, called ribosomopathies are associated with various cancers. The ribosomal small subunit processome (SSU processome) is a large ribonucleoprotein complex responsible for the assembly of the SSU of the ribosome. It consists of five sub-complexes, one of which (the UTP-C) is believed to contain the protein kinase/casein kinase CK2 complex. It consists of two catalytic (CKα/a1 and CKαʹ/a2) and two regulatory (CKβ/b1 and CKβʹ/b2) proteins. CK2 is a ubiquitous and constitutively active serine/threonine kinase. Our objective is to validate the membership of CK2 in the SSU processome and to determine the contribution of CK2 to the regulation of ribosome assembly and growth.
Using a yeast model, we built strains capable of conditional depletion of individual and pairs of CK2 proteins, with growth used as a surrogate for ribosome assembly.
Depletion of individual catalytic subunits CKa1 and CKa2 results in a reduction in growth, while simultaneous depletion of both catalytic subunits is lethal, as seen by an arrest in growth. Northern analysis of pre-rRNA processing will be used to identify a slowing or defect in ribosome assembly. In contrast, single and double depletion of the regulatory CKb1 and CKb2 proteins showed no change in growth. Membership of CK2 in the SSU processome will be confirmed by co-IP of each of the individual CK2 proteins with the known SSU processome components Mpp10 and U3 snoRNA.
Thus, we have shown that single and double depletion of the two catalytic CK2 proteins has a major impact on cell growth, likely through a dysregulation of ribosome assembly.